Bromine (CHEM000132)

Elemental bromine exists as a diatomic molecule, Br2. It is a dense, mobile, slightly transparent reddish-brown liquid, that evaporates easily at standard temperature and pressures to give an orange vapor (its color resembles nitrogen dioxide) that has a strongly disagreeable odor resembling that of chlorine. It is one of only two elements on the periodic table that are known to be liquids at room temperature (the other being mercury). Bromine is corrosive and toxic, with properties between those of chlorine and iodine. Free bromine does not occur in nature, but occurs as colorless soluble crystalline mineral halide salts, analogous to table salt. Bromine is used in the preparation of brominated flame retardants, it is also used in the preparation of gas additives and pesticides. Bromide compounds, especially potassium bromide, were frequently used as general sedatives in the 19th and early 20th century. Bromides in the form of simple salts are still used as anticonvulsants in both veterinary and human medicine, although the latter use varies from country to country. Bromine has been long believed to have no essential function in mammals, but recent research suggests that bromine is necessary for tissue development. In addition, bromine is used preferentially over chlorine by one antiparasitic enzyme in the human immune system. Organobromides are needed and produced enzymatically from bromide by some lower life forms in the sea, particularly algae.